Alluvial and gypsum karst geological transition favors spreading arsenic contamination in Matehuala, Mexico

[Display omitted] •Arsenic contamination in Matehuala is mostly linked to a shallow aquifer.•Shallow lithosphere configuration plays a key role in arsenic transport in Matehuala.•Exposure to arsenic contaminated groundwater causes accumulation in human hair.•Arsenic transport is more rapid and extent in a gypsum karst than in alluvial aquifers. Arsenic transport in alluvial aquifers is usually constrained due to arsenic adsorption on iron oxides. In karstic aquifers, however, arsenic contamination may spread to further extensions mainly due to favorable hydrogeochemical conditions. In this study, we i) determined the spatial and temporal behavior of arsenic in water in an alluvial-karstic geological setting using field and literature data, ii) established whether a contaminated aquifer exists using field and literature piezometric data and geophysical analysis, iii) studied the local geology and associated arsenic contaminated water sources to specific aquifers, iv) revealed and modeled subsoil stratigraphy, and v) established the extent of arsenic exposure to the population. We found arsenic contamination (up to 91.51 mg/l) in surface and shallow groundwater (